linux-kernel - Re: [PATCH] ARM: dts: Add Raspberry Pi Compute Module 4 CANOPi Board

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Message-ID: <4e378923-6107-2ed3-3bc2-31e861f525f1@i2se.com>
Date:   Tue, 20 Sep 2022 17:41:16 +0200
From:   Stefan Wahren <stefan.wahren@...e.com>
To:     Ariel D'Alessandro <ariel.dalessandro@...labora.com>,
        bcm-kernel-feedback-list@...adcom.com, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-rpi-kernel@...ts.infradead.org, arnd@...db.de,
        f.fainelli@...il.com, nsaenz@...nel.org, olof@...om.net,
        robh+dt@...nel.org, soc@...nel.org, william.zhang@...adcom.com,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
Subject: Re: [PATCH] ARM: dts: Add Raspberry Pi Compute Module 4 CANOPi Board

Hi Alexander,

Am 20.09.22 um 10:31 schrieb Alexander Dahl:
> Hello Stefan,
>
> Am Mon, Sep 19, 2022 at 01:18:21PM +0200 schrieb Stefan Wahren:
>> Hi Alexander,
>>
>> [fix address of Krzysztof]
>>
>> Am 19.09.22 um 09:47 schrieb Alexander Dahl:
>>> Hei hei,
>>>
>>> Am Fri, Sep 16, 2022 at 12:31:56PM -0300 schrieb Ariel D'Alessandro:
>>>> The Eclipse KUKSA CANOPi [0] is a baseboard for the Raspberry Compute
>>>> Module 4 (CM4). It contains a VIA VL805 4 Port USB controller and two
>>>> MCP251xFD based CAN-FD interfaces.
>>>>
>>>> [0] https://github.com/boschresearch/kuksa.hardware
>>>>
>>>> Signed-off-by: Ariel D'Alessandro <ariel.dalessandro@...labora.com>
>>>> ---
>>>>    arch/arm/boot/dts/Makefile                    |   1 +
>>>>    arch/arm/boot/dts/bcm2711-rpi-cm4-canopi.dts  | 139 ++++++++++++++++++
>>>>    arch/arm64/boot/dts/broadcom/Makefile         |   1 +
>>>>    .../dts/broadcom/bcm2711-rpi-cm4-canopi.dts   |   2 +
>>>>    4 files changed, 143 insertions(+)
>>>>    create mode 100644 arch/arm/boot/dts/bcm2711-rpi-cm4-canopi.dts
>>>>    create mode 100644 arch/arm64/boot/dts/broadcom/bcm2711-rpi-cm4-canopi.dts
>>>>
>>>> diff --git a/arch/arm/boot/dts/Makefile b/arch/arm/boot/dts/Makefile
>>>> index 05d8aef6e5d2..8930ab2c132c 100644
>>>> --- a/arch/arm/boot/dts/Makefile
>>>> +++ b/arch/arm/boot/dts/Makefile
>>>> @@ -98,6 +98,7 @@ dtb-$(CONFIG_ARCH_BCM2835) += \
>>>>    	bcm2837-rpi-zero-2-w.dtb \
>>>>    	bcm2711-rpi-400.dtb \
>>>>    	bcm2711-rpi-4-b.dtb \
>>>> +	bcm2711-rpi-cm4-canopi.dtb \
>>>>    	bcm2711-rpi-cm4-io.dtb \
>>>>    	bcm2835-rpi-zero.dtb \
>>>>    	bcm2835-rpi-zero-w.dtb
>>>> diff --git a/arch/arm/boot/dts/bcm2711-rpi-cm4-canopi.dts b/arch/arm/boot/dts/bcm2711-rpi-cm4-canopi.dts
>>>> new file mode 100644
>>>> index 000000000000..52ec5908883c
>>>> --- /dev/null
>>>> +++ b/arch/arm/boot/dts/bcm2711-rpi-cm4-canopi.dts
>>>> @@ -0,0 +1,139 @@
>>>> +// SPDX-License-Identifier: GPL-2.0
>>>> +/dts-v1/;
>>>> +#include "bcm2711-rpi-cm4.dtsi"
>>>> +
>>>> +/ {
>>>> +	model = "Raspberry Pi Compute Module 4 CANOPi Board";
>>>> +
>>>> +	clocks {
>>>> +		clk_mcp251xfd_osc: mcp251xfd-osc {
>>>> +			#clock-cells = <0>;
>>>> +			compatible = "fixed-clock";
>>>> +			clock-frequency = <20000000>;
>>>> +		};
>>>> +	};
>>>> +
>>>> +	leds {
>>>> +		led-act {
>>>> +			gpios = <&gpio 42 GPIO_ACTIVE_HIGH>;
>>>> +		};
>>>> +
>>>> +		led-pwr {
>>>> +			label = "PWR";
>>>> +			gpios = <&expgpio 2 GPIO_ACTIVE_LOW>;
>>>> +			default-state = "keep";
>>>> +			linux,default-trigger = "default-on";
>>>> +		};
>>>> +	};
>>> This looks like using the node name and the deprecated "label"
>>> property for LED naming.  Please see
>>> Documentation/devicetree/bindings/leds/common.yaml and use the
>>> properties "function" and "color" instead.  Also check the node names
>>> itself, see the example in that binding or the leds-gpio binding for
>>> reference.
>> Oops, i didn't noticed this.
>>
>> Unfortunately the ACT-LED is already a little bit opaque defined in
>> bcm2835-rpi.dtsi:
>>
>> leds {
>>          compatible = "gpio-leds";
>>
>>          led-act {
>>              label = "ACT";
>>              default-state = "keep";
>>              linux,default-trigger = "heartbeat";
>>          };
>> };
>>
>> So a reference (currently missing) would have make it clear that the ACT-LED
>> is common for all Raspberry Pi boards.
> Yes, a reference would probably good, would make it easier to spot
> this is already defined in the dtsi.
I will take care of this.
>
>> So you wish that this is fixed for the CANOPi board or all Raspberry Pi
>> boards?
>>
>> I'm asking because switching to function would change the sysfs path and
>> breaking userspace ABI.
> You're right, and the effective label should stay as is for existing
> boards to not break userspace.
>
> Not sure what the policy is for baseboards with compute modules.  Are
> those LEDs on the compute module?  Or does the CM just expose those
> GPIOs?
These are GPIOs expose by the Compute Module. Since these are 
initialized by the VC4 firmware, it's not the best idea to use them for 
other functions.
>    Is there some policy all baseboards must use them for LEDs?
> An what about additional LEDs on the baseboard?  Is this allowed?
Definitely
> (I don't think there a generic rules for that, but maybe some best
> practices for certain SoMs like the RPi CM?)
I think we should for Ariel's reponse.
> IMHO for new independent boards though, new LEDs should not be
> introduced the old way. I thought this is the case here, but it seems
> I was wrong due to that baseboard vs. SoM thing.

Without your comment i hadn't noticed this :-)

I'm thinking of a dtsi file in order to encapsulate the deprecated LED 
stuff, remove the global ACT-LED from bcm2835-rpi.dtsi and include the 
dtsi from all board files.

Best regards